The present invention relates generally to medical devices and methods. More specifically, the invention relates to devices and methods for stabilizing and ablating body tissues, such as cardiac tissue, to treat various conditions, such as atrial fibillation.
Atrial fibrillation (AF) is a heart beat rhythm disorder in which the upper chambers of the heart known as the atria quiver rapidly, instead of beating in a steady rhythm. This rapid quivering reduces the heart's ability to properly function as a pump. AF is characterized by circular waves of electrical impulses that travel across the atria in a continuous cycle. It is the most common clinical heart arrhythmia, affecting more than two million people in the United States and some six million people worldwide.
Atrial fibrillation typically increases the risk of acquiring a number of potentially deadly complications, including thrombo-embolic stroke, dilated cardiomyopathy and congestive heart failure. Quality of life is also impaired by common AF symptoms such as palpitations, chest pain, dyspnea, fatigue and dizziness. People with AF have, on average, a five-fold increase in morbidity and a two-fold increase in mortality compared to people with normal sinus rhythm. One of every six strokes in the U.S. (some 120,000 per year) occurs in patients with AF, and the condition is responsible for one-third of all hospitalizations related to cardiac rhythm disturbances (over 360,000 per year), resulting in billions of dollars in annual healthcare expenditures.
AF is the most common arrhythmia seen by physicians, and the prevalence of AF is growing rapidly as the population ages. The likelihood of developing AF increases dramatically as people age; the disorder is found in about 1% of the adult population as a whole, and in about 6% of those over age 60. By age 80, about 9% of people (one in 11) will have AF. According to a recent statistical analysis, the prevalence of AF in the U.S. will more than double by the year 2050, as the proportion of elderly increases. A recent study called The Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) study, published in the Spring of 2001 in the Journal of the American Medical Association (JAMA), found that 2.3 million U.S. adults currently have AF and this number is likely to increase over the next 50 years to more than 5.6 million, more than half of whom will be age 80 or over.
As the prevalence of AF increases, so will the number of people who develop debilitating or life-threatening complications, such as stroke. According to Framingham Heart Study data, the stroke rate in AF patients increases from about 3% of those aged 50-59 to more than 7% of those aged 80 and over. AF is responsible up to 35% of the strokes that occur in people older than age 85.
Efforts to prevent stroke in AF patients have so far focused primarily on the use of anticoagulant and antiplatelet drugs, such as warfarin and aspirin. Long-term warfarin therapy is recommended for all AF patients with one or more stroke risk factors, including all patients over age 75. Studies have shown, however, that warfarin tends to be under-prescribed for AF. Despite the fact that warfarin reduces stroke risk by 60% or more, only 40% of patients age 65-74 and 20% of patients over age 80 take the medication, and probably fewer than half are on the correct dosage. Patient compliance with warfarin is problematic, and the drug requires vigilant blood monitoring to reduce the risk of bleeding complications.
Electrophysiologists classify AF by the “three Ps”: paroxysmal, persistent, or permanent. Paroxysmal AF—characterized by sporadic, usually self-limiting episodes lasting less than 48 hours—is the most amenable to treatment, while persistent or permanent AF is much more resistant to known therapies. Researchers now know that AF is a self-perpetuating disease and that abnormal atrial rhythms tend to initiate or trigger more abnormal rhythms. Thus, the more episodes a patient experiences and the longer the episodes last, the less chance of converting the heart to a persistent normal rhythm, regardless of the treatment method.
AF is characterized by circular waves of electrical impulses that travel across the atria in a continuous cycle, causing the upper chambers of the heart to quiver rapidly. At least six different locations in the atria have been identified where these waves can circulate, a finding that paved the way for maze-type ablation therapies. More recently, researchers have identified the pulmonary veins as perhaps the most common area where AF-triggering foci reside. Technologies designed to isolate the pulmonary veins or ablate specific pulmonary foci appear to be very promising and are the focus of much of the current research in catheter-based ablation techniques.
Currently available devices and methods, however, do not provide ideal means for cardiac stabilization and ablation of epicardial tissue in advantageous patterns for treating AF. Although many ablation devices and stabilization devices are currently available, combining stabilization and ablation features into one device to allow ablation of epicardial tissue in a desired pattern on a beating heart has proven challenging. Typically, therefore, current cardiac ablation procedures for AF treatment still require stopping the heart and using a cardiopulmonary bypass apparatus.
Therefore, a need exists for devices and methods to enhance minimally invasive techniques for ablating cardiac tissue to treat AF. Preferably, such devices and methods would provide ablation in one or more patterns on the epicardial surface of the heart, such as in a pattern adjacent to or surrounding one or more pulmonary veins. Also preferably, the devices and methods would provide stabilization of the heart as well as ablation, to allow for minimally invasive ablation procedures without cardiopulmonary bypass. At least some of these objectives will be met by the present invention.